The structural incompatibility between the two vessels allowed the ferry to impact upon and severely damage the tug's superstructure. While the tug was manoeuvring into position, it was inadvertently pushed to port and off its heading by the ferry's propeller wash and then pushed further by the ferry's port quarter, which unexpectedly swung out towards the tug. The bridge team on the ferry was not fully aware of the tug's position.Findings as to Causes and Contributing Factors The structural incompatibility between the two vessels allowed the ferry to impact upon and severely damage the tug's superstructure. While the tug was manoeuvring into position, it was inadvertently pushed to port and off its heading by the ferry's propeller wash and then pushed further by the ferry's port quarter, which unexpectedly swung out towards the tug. The bridge team on the ferry was not fully aware of the tug's position. There was no protocol for the profile of the tug to be matched to that of the vessel it was assigned to assist.Finding as to Risks There was no protocol for the profile of the tug to be matched to that of the vessel it was assigned to assist.